MOSCOW -- At least 33 people died in two explosions in Volgograd, South Russia, on Sunday and Monday. The proximity to North Caucasus and the Black Sea resort of Sochi, where the 2014 Winter Olympics will be held in six weeks, has raised concerns over safety issues at the global sports event, which is expected to attract the world's media and put the spotlight on Russia.

Within less than 20 hours, two bombings took place in Volgograd. On Sunday, a suicide bomb attack occurred at the city's main train station, killing 18 and injuring over 40 people. During the morning rush hour on Monday, a second bomb attack was carried out on a trolley bus moving from a residential neighborhood to the city center, killing 15, the Russian wire service Interfax reported.

The recent terrorist attacks in Volgograd come just over two months after another bombing in the city in which seven people were killed and 55 wounded when an explosive went off on a city bus on Oct. 21. At the time, some feared the attack could have been terrorists' "test shot" as they plot more attacks for the Winter Olympics.

The October explosion was carried out by 30-year old Naida Asiyalova, a native of the North Caucasian republic of Dagestan and so-called "black widow" -- a wife of a slain Islamist terrorist.

According to early reports, the train station attack may have been carried out by another black widow, 26-year old Oksana Aslanova. Later, Interfax quoted security sources as saying they also suspect a Slavic man could have brought in the explosives by backpack.

Russia's Investigative Committee said in a statement on its website that the two recent terrorist attacks in Volgograd are likely to be connected, although various versions of events are being considered. Earlier, there were reports about possible connections between the October bus bombing and the train station attack.

The Russian media have linked the recent Volgograd terrorist attacks to the upcoming Olympics.

"The biggest danger is that the [Islamist] fighters are apparently trying to turn attention away from the situation in Sochi," wrote a commentator for Yezhednevny Zhurnal. "They want to show security services that more resources will have to be allocated to ensure safety not only at the Olympic venues, but also outside that region, as terrorists could strike elsewhere, as well."

The International Olympics Committee expressed its condolences over Sunday's bombing in Volgograd but said it was confident of Russia's ability to protect the Games.

IOC president Thomas Bach told the Associated Press that he has full confidence that Russian authorities will pull off a "safe and secure" games.

Bach tells the AP he is "certain that everything will be done to ensure the security of the athletes and all the participants of the Olympic Games."

Russian Olympic Committee chief Alexander Zhukov said Monday there was no need to take any extra steps to secure Sochi in the wake of the Volgograd bombings, as "everything necessary already has been done."

Russian authorities have introduced some of the most extensive identity checks and sweeping security measures ever seen at an international sports event.

The security zone created around Sochi stretches approximately 100 kilometers (60 miles) along the Black Sea coast and up to 40 kilometers (25 miles) inland.

Russian forces include special troops to patrol the forested mountains flanking the resort, drones to keep constant watch over Olympic facilities and speed boats to patrol the coast.

Anyone wanting to attend the games that open on Feb. 7 will have to buy a ticket online from the organizers and obtain a "spectator pass" for access. Doing so will require providing passport details and contacts that will allow the authorities to screen all visitors. The security plan includes a ban on cars from outside the zone a month before the games begin.